A known multiplying device includes a pneumatic cylinder which is filled by pressurized fluid in order to move a reciprocating piston. The bottom of the cylinder is closed by a lower cap. Nevertheless, most of such pressure multiplying devices comprise piston-cylinder assemblies capable of generating hydraulic pressure in only one of the two strokes of the piston. The multiplying devices, through structural limitations, only produce pressure during either the back-stroke or the forward stroke, but never in both successive piston strokes.
As stated before, the prior art hydraulic pressure multiplying devices were used to generate pressure in only one stroke of the piston. This results in several disadvantages, one of which is that the pressurized flow has a rather low frequency cycle. Furthermore the single-effect pressure multiplying devices of the prior art, which are used for operating the crimping means of tool machines, are provided with strong springs for driving the fluid compressing piston in its backward stroke. This is neccesary for allowing the crimping means to come to its rest position for releasing the piece already machined. Sometimes it is necessary to provide big and heavy springs, and the space or volume they occupy may be considerable.